The invention relates to a hemodialysis device with a dialyzer which has two chambers separated by a membrane, of which one is switched into a dialyzing liquid path and the other into a blood path, with a dialyzing liquid source, with a suction pump arranged in the dialyzing liquid path and controlling the transmembrane pressure, with a restrictor apparatus arranged upstream of the dialyzer in the dialyzing liquid path, with a change-over valve interposed downstream of the suction pump in the dialyzing liquid path, with a line going off from the change-over valve and returning to the dialyzing liquid path upstream of the dialyzer, with a volume measuring apparatus connected to the dialyzing liquid path for measurement of the volume of the ultrafiltered liquid quantity, with an apparatus for determination of the transmembrane pressure in the dialyzer and with a control apparatus which is connected to the unit for determination of the transmembrane pressure and controls the suction pump.
The homodialysis device mentioned at the start, or artificial kidney, is intended to remove substances normally contained in the urine and to regulate the liquid, electrolyte and acid-base equilibria.
Even if there are initial moves to perform this regulation on the basis of objective, physiological parameters which can be measured continuously, for example by continuous measurement of the hematocrit in the extracorporeal circulation, dialysis is still craried out today exclusively on the basis of empirically established ideal or set values (cf. ASAIO 7 (1983), p. 410). The bulk of the units in use today do not even allow the parameters given by the physician to be maintained precisely, let alone allow specific control of these units.
An area in which certain progress has been made is in the field of ultrafiltration control, in which to an increasing extent so-called volume-controlled dialysis units are being used, which allow an exact ultrafiltration, provided that certain preconditions are met regarding the technical aspects of the apparatus. In the case of such devices, ultrafiltration is performed in a closed volume of dialyzing liquid which is periodically changed. Only in such a closed system, of which the A 2008 C dialysis unit of the applicant is an actual example, is it ensured that accurate ultrafiltration control can be carried out.
On the other hand, for reasons of cost, in many countries simple single-pass units are still in use which currently cannot be changed although the advantages of volume-controlled devices for the patient are sufficiently demonstrated and recognized.
Consequently, it has been necessary to develop devices through which the known simple hemodialysis devices can be verified and adjusted.
The transfer of liquid from the blood circuit to the dialyzing liquid circuit, ie. the ultrafiltered liquid, can be performed by devices both on the blood side and on the dialyzing liquid side. The following processes for this are known:
As already mentioned above, a volume control can be ensured by a balancing device, which ensures that the liquid quantities flowing to and from the dialyzer are equal. The quantity to be ultrafiltered is withdrawn from this balancing device by an additional apparatus, namely an ultrafiltrate pump, so that finally the ultrafiltrate can be determined exactly. Such a device is known for example from German Offenlegungsschrift No. 28 38 414.
Furthermore, a relative flow measurement of the liquid quantities flowing to and from the dialyzer, ie. the quantities of blood or in particular dialyzing liquid, can be performed. By use of the properties of difference formation per unit of time, comparison with a pre-set rate and control of the transmembrane pressure, the desired rate can be achieved. This principle is realized, for example, on the dialyzing liquid side by the UFM-2 ultrafiltration module of the Gambro Company. For the blood side, such a device is specified in German Auslegeschrift No. 33 13 421.
Another process comprises measuring the ultrafiltration coefficient. As is known, this changes from dialyzer to dialyzer due to deviations of a technical production nature and in particular during the course of dialysis, since the membranes change or the pores become blocked. Consequently, the ultrafiltration quantity also changes, regularly becoming less per unit of time in the course of dialysis. Therefore, the ultrafiltration coefficient must be determined discontinuously in the course of dialysis, keeping this measuring period of the transmembrane pressure TMP constant. This is the case with the hemofiltration units COBE CENTRY 2000 or Braun UF Module.
On the other hand however, the ultrafiltration rate can be given and the self-adjusting mean TMP becoming can be From the UF rate and the TMP in turn, the UF coefficient can be calculated and consequently the TMP can be controlled in such a way that the preset UF rate is attained.
German Patent Specification No. 25 48 759 discloses a dialysis unit with which the ultrafiltration rate can be measured at any time during the blood dialysis treatment and the dialysate pressure can be kept at a value which is adapted to a pressure adjusted in the dialyzer. This arrangement works with a pump in both the supply line and in the discharge line of the dialyzing liquid, these pumps being driven by a common motor and having the same displacement capacity.
Apart from the fact that this arrangement requires highly elaborate apparatus, in addition it is also not adequately accurate as such pumps have an error in their displacement capacity of about 2%. If the thought is considered that about 2% of the dialyzing liquid quantities flowing through the dialyzer are additionally to be withdrawn as ultrafiltration quantity, it is already apparent that no accurate ultrafiltration can be carried out with such an arrangement and in some cases the use of such an arrangement may even be critical for the patient.
German Offenlegungsschrift No. 32 02 831 discloses a hemodialysis device of the type first mentioned above in which the open circuit in a single-pass device is closed for the duration of measurement of the withdrawn ultrafiltrate quantity and the withdrawn ultrafiltrate quantity is determined in a volume measuring apparatus as a function of the measuring period. The known dialysis apparatus is disadvantageous inasmuch as it requires a highly elaborate apparatus to be able to determine this measured value exactly. This results in a possibility of error accumulation, so that it is desirable to use a less error-susceptible device.
In the hemodialysis device according to German Offenlegungsschrift No. 32 02 831, this disadvantage results initially from the fact that a further pump has to be provided in the dialyzing liquid source, absolutely necessary for displacing the dialyzing liquid into the dialyzing liquid circuit. If, for example, a dialyzing liquid of incorrect composition is produced, a dialysis unit usually has a protective system which takes care that the dialyzing liquid of incorrect composition is displaced past the dialyzer into a bypass line into the drain.
Furthermore, this known dialysis device has a displacement pump in connection with a restrictor which is designed as a constant flow apparatus and which is intended to adjust a certain transmembrane pressure in conjunction with the suction pump arranged downstream of the dialyzer. Due to the usual rate of inaccuracy of about 2% which can be established for such a pump, such a device must be switched to measuring operation relatively frequently, which leads to interruption of treatment of the patient. Added to this is that, with an increasing number of pumps used in such a dialysis device and number of valve arrangements, the error susceptibility and the inaccuracy of such a hemodialysis device increases, which is undesirable.
Furthermore, in this known hemodialysis device, the volume measuring apparatus branches off directly from the dialyzing liquid circuit downstream of the dialyzing liquid source, which has the disadvantage during a relatively long measuring period that the dialyzing liquid cools down, with the consequence that the patient may freeze to death during dialysis treatment.
German Offenlegungsschrift No. 23 28 593, corresponding to U.S. Pat. No. 3,979,284 to Granger et al., and German Offenlegungsschrift No. 13 29 26 681 disclose hemodialysis devices in which the dialyzing liquid circuit is completely closed for determination of the transmembrane pressure at a certain ultrafiltration rate, an exactly volumetrically working pump being connected to this closed circuit. This additional pump initially increases the costs and the error susceptibility of such a device. Measurement of the transmembrane pressure is made in this case using a given pump rate with which then in turn a further pump, acting as suction pump, is controlled.
In general, the known hemodialysis devices have the disadvantage that they have a separate disinfection program to prevent the patient being connected unintentionally to the disinfectant solution, with fatal effect. Consequently, the known devices have manually fitted dialysis plugs which, once the dialysis device has been switched off, have to be plugged into appropriate sockets in the dialysis device in order to disinfect the entire device.